This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-264540, filed Sep. 17, 1999; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a stencil printing machine of an inner pressure type for acting a printing pressure onto the inner peripheral surface of a printing drum.
2. Description of the Related Art
There is a conventional stencil printing machine of the inner pressure type that has been disclosed in the Japanese laid-open publication No. 10-100528, for example.
FIG. 1 is a partially sectional view of the conventional stencil printing machine of the above example. In FIG. 1, the parts of the outer peripheral surfaces of both a printing drum 100 and a pressure roller 101 are rotatably arranged in close proximity to each other. The peripheral surface of the printing drum 100 is made up of a screen. A stencil sheet 103 can be fitted on and removed from the outer peripheral surface of a screen 102.
An inner press roller 104 is arranged or placed in the printing drum 100 so that the inner press roller 104 is rotatable around a lever 106 that is supported around the center of a supporting shaft 105. The inner press roller 104 is moved between the standby position and the pressure position A. The standby position is separated in arrangement from the inner peripheral surface of the screen 102. At the pressure position A, the inner press roller 104 presses the inner peripheral surface of the screen 102. An inner press mechanism 107 is arranged in the printing drum 100.
The inner press mechanism 107 comprises an inner press roller shift means 108 and a pressure adjustment means 109 for the inner press roller 104. The inner press roller shift means 108 provides a driving power to the lever 106 so that the inner press roller 104 can be shifted between the standby position and the pressure position A. The pressure adjustment means 109 for the inner press roller 104 can adjust the pressure power of the inner press roller 104 at the pressure position A.
The inner press roller shift means 108 has a shifting motor 110 whose rotation shaft is fixed to a first gear 111. This first gear 111 is meshed with a second gear 112 correctly. In addition, an eccentric cam 113 is fixed to the second gear 112. The cam surface of the eccentric cam 113 contacts with a cam follower 114 that is supported rotatably by a lever 106. When the shifting motor 110 is rotating, this rotation is transmitted to the eccentric cam 113 through the first and second gears 111 and 112. Then, the lever 106 rotates according to the rotation position of the eccentric cam 113, so that the inner press roller 104 is shifted between the standby position and the pressure position A shown in FIG.1.
The pressure adjustment means 109 for the inner press roller 104 has the adjustment motor 115 whose rotation shaft is fixed to a third gear 116. The third gear 116 and a fourth gear 117 are meshed. A nut member 118 is fixed to this fourth gear 117. A screw rod 119 is inserted to the threaded hole of this nut member 118, and one end of a screw rod 119 is connected to one end of a spring 121 through an arm member 120.
Other end of this spring 121 is connected to the lever 106 and the inner press roller 104 may press the screen 102 by the pressure of the spring 121. When the adjustment motor 115 rotates, this rotation is transmitted to the screw rod 119 in order to rotate the screw rod 119 through the third gear 116, the fourth gear 117, and the nut member 118. The screw rod 119 is thereby shifted toward the shaft direction thereof and a stroke of the spring 121 is changed in order to adjust the pressure power of the inner press roller 104.
Next, a description will be given to an outline of the operation of the conventional stencil printing machine.
After perforations for printing a desired image pattern are made on the stencil sheet 103, the perforated stencil sheet 103 (hereinafter, also referred to as the stencil sheet) is set up on the peripheral surface of the screen 102 forming the wall of the printing drum 100 by clamping the leading edge of the stencil sheet 103.
Next, the inner press roller 104 is shifted to the pressure position A from the standby position by the inner press roller shiftmeans 108 and then both the printing drum 100 and the pressure roller 101 rotate simultaneously. Then, the inner press roller 104 presses the screen 102, and in this state, the inner press roller 104 also rotates following the rotation of the printing drum 100. Ink is supplied on the outer peripheral surface of the inner press roller 104. Then, the ink adhered on the outer peripheral surface of the inner press roller 104 is moved onto the screen in turn.
In this situation, as shown in FIG.1, the print paper 122 is fed between the printing drum 100 and the pressure roller 101 and also continuously fed by the rotation of both the printing drum 100 and the pressure roller 101. The print paper 122 between the printing drum 100 and the pressure roller 101 is fed to outside while pressing the print paper 122, the screen 102, and the stencil sheet 103 between the inner press roller 104 and the pressure roller 101.
The ink of the image pattern on the screen 102 is moved (or printed) from the perforations on the stencil sheet 103 onto the print paper 122 according to the stencil pattern on the stencil sheet 103. Because the print concentration on the print paper 122 is proportional to the pressure of the inner press roller 104, the pressure of the inner press roller 104 may be adjusted by the pressure adjustment means 109 for the inner press roller 104 in order to adjust the concentration of the print on the print paper 122.
However, because the inner press mechanism 107 is arranged in the printing drum 100 in the conventional stencil printing machine having the configuration shown in FIG. 1, it is impossible to reduce the diameter of the printing drum 100 as small as possible. That is, for example, although the stencil printing machine of a small size using small-sized print papers can be obtained by reducing the diameter of the printing drum 100, it is impossible to reduce the stencil printing machine having the configuration where the whole body of the inner press mechanism 107 is contained in the printing drum 100.
In the light of the above mentioned situations, the present invention has been made. An object of the present invention is, with due consideration to the drawbacks of the conventional technique, to provide a stencil printing machine having a small sized configuration by reducing the diameter of a printing drum thereof.
In accordance with a preferred embodiment of the present invention, a stencil printing machine has a printing drum, a pressure drum, a stencil sheet, an inner press roller, and an inner press mechanism. The outer peripheral surfaces of both the printing drum and the pressure drum are close to each other and rotatable independently. The stencil sheet is attached-on and removable from an outer peripheral surface of the printing drum. The inner press roller is arranged in an inner peripheral surface side of the printing drum, and is shifted between a pressure position at which the inner press roller presses the inner peripheral surface of the printing drum, and a standby position at which the inner press roller is separated in position from the inner peripheral surface. The inner press mechanism adjusts a pressure power of the inner press roller at the pressure position and which comprises an ink supply unit and a power transfer means. The ink supply unit is arranged at inside of the printing drum for shifting the inner press roller between the pressure position and the standby position. The power transfer means is arranged at outside of the printing drum, and provides a driving power to the ink supply unit in order to shift the inner press roller between the pressure position and the standby position and in order to adjust the pressure power of the inner press roller at the pressure position. In the stencil printing machine, during printing, both the printing drum and the pressure drum are rotated so that the outer peripheral surfaces, which are close to each other, of both the printing drum and the pressure drum rotate in a same direction, and the stencil printing is performed by pressing a print paper which is fed between the pressure drum and the stencil sheet placed on the surface of the printing drum by the pressure power. Accordingly, the present invention has a feature in which the power transfer means is arranged at the outside of the printing drum, and the ink supply unit is arranged at the inside of the printing drum.
In addition, in the stencil printing machine as another preferred embodiment of the present invention, the power transfer means has a combined power means for receiving the driving power from a single driving power source in order to shift the inner press roller between the pressure position and the standby position and in order to adjust the pressure power of the inner press roller at the pressure position. Accordingly, one driving power source can perform to shift the inner press roller between the standby position and the pressure position and to adjust the pressure of the inner press roller, and a common power transfer system can be used other than the combined power means.
In addition, in the stencil printing machine as another preferred embodiment of the present invention, the combined power source has a link member and a spring for connecting the driving power source with the ink supply unit, and the link member transfers the driving power to the ink supply unit during a shift operation of the inner press roller from the pressure position to the standby position, and the spring transfers the driving power to the ink supply unit during a shift operation of the inner press roller from the standby position to the pressure position. Accordingly, the combined power means can be made by using the link member and the spring.
Furthermore, in the stencil printing machine as another preferred embodiment of the present invention, both the printing drum and the pressure drum has a same diameter.
Moreover, in the stencil printing machine as another preferred embodiment of the present invention, the single driving power source as the power transfer mean made up of a motor.